What does Luke 8:30 mean?

Demons have possessed a man who is now speaking with Jesus. Jesus has commanded them to leave, and they're afraid He's going to imprison them in the abyss (Luke 8:26–29, 31). Now, Jesus asks for their name.

Mary Magdalene had been freed from seven demons (Luke 8:2). This man is beset by a legion. A "legion" was a Roman military unit of varied numbers. In some cases, it could include as many as six thousand troops. Mark notes the demons destroy a herd of about two thousand pigs (Mark 5:13). In modern English, the demons might have claimed a name like "Battalion," or "Brigade." The term is appropriate both for their number and for the war image: this is a battle for the man's life.

Demons seem to have different amounts of power. Although the disciples expel other demons (Luke 10:17), they cannot free a young boy (Luke 9:40). The Sons of Sceva use the mantra "I adjure you by the Jesus whom Paul proclaims," but a particularly powerful demon overpowers them, beats them, and rips off their clothes (Acts 19:13–16). We don't know how powerful this man's demons are individually, but as a group they feel emboldened to delay obeying Jesus' order to release the man just long enough to negotiate an exit strategy.

It's unclear why Jesus asks the demons their name. In some spiritual traditions, knowing another's name grants power over them. Jesus might have been playing on that stereotype without necessarily agreeing with it. There's no biblical foundation for the idea itself; Jesus exorcises the powerful demon who possesses the boy without mentioning its name (Luke 9:37–43). It may be that Jesus is revealing to His disciples that the man is possessed by a great number of demons.